Discovered a potential bug today that will slightly boost audio (by less than 1 dB) when exporting through AE's Render Queue 'H264 - Match Render Settings - 5Mbps' Output Module preset. This resulted in clipped audio (hitting reds) in my final output. Audio was an unchanged WAV music track that was quite heavily limited (metal genre).
I was able to solve the issue by exporting the comp to ProRes 422, importing to a new Premiere timeline and exporting to H264. This gave me an H264 at 5mbps that did not clip.
I expect this is likely due to mp3 compression, and may be known to low H264 bitrates, however thought it odd that the problem did not occur when exporting with the *same* settings and bitrate from Premiere.
Note: I did not try to repeat the bug via Media Encoder (don't ask me why - was on a tight deadline and went on autopilot as there were a couple different variations of the export - Prem was quicker in this instance).
Thank you for reporting this issue. There was a similar bug, related to low bitrates for H264 audio, reported and fixed in the latest After Effects 23.1 release. Would you please try this again in that version and let us know if you still are experiencing the issue?
Thanks for reporting this issue and for any further information you can provide,